Which one of the following statements is/are correct?
A. Gallium has higher ionisation enthalpy than aluminium
B. Boron does not exist as `B^(3+)` ion
C. Aluminium forms `[AIF_(6)]^(3-)` ion but boron does not form `[BF_(6)]^(3-)` ion
D. Tl `(NO_(3))_(3)` acts as an oxidising agent.